1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a storage medium storing program that causes a computer to execute the image processing method.
2. Description of the Related Art
In the medical field, a physician displays a medical image including a captured subject (e.g., a three-dimensional image composed of a tomographic image group that represents three-dimensional internal information of the subject) on a monitor, and diagnoses a lesion while reading the displayed medical image. A medical image collection apparatus that can capture a group of tomographic images is generally referred to as a “modality.” For example, representative modalities include an ultrasonic image diagnosing apparatus (e.g., an ultrasonic image capturing apparatus), a magnetic resonance imaging apparatus (hereinafter, referred to as “MRI apparatus”), and an X-ray computer tomographic imaging apparatus (hereinafter, referred to as “X-ray CT apparatus”).
It is generally difficult for a physician to accurately diagnose the state of a lesion while observing a group of tomographic images captured by these modalities. Hence, performing a comparison with respect to a concerned lesion between tomographic image groups captured by different modalities (or differentiated in captured date and time) has been conventionally tried to improve the accuracy in the diagnosis of the lesion state.
To utilize a plurality of types of tomographic image groups in a diagnostic operation, it is important to perform matching between respective tomographic image groups with respect to a lesion of interest. It is generally difficult to realize an automatic matching based on image processing due to various influences (including differences in respective modalities and deformation of the subject). Therefore, an operator (e.g., a physician) generally performs a manual matching work while viewing corresponding images. In this case, while viewing a lesion of interest indicated in one image group, the operator identifies a portion corresponding to the lesion (i.e., a corresponding lesion) in the other image group with reference to the similarity in the shape of the lesion or its peripheral portion. Trials to support the above-described matching work have been conventionally conducted.
For example, as discussed in Japanese Patent Application Laid-Open No. 2008-246264, it is conventionally feasible to support the search of a corresponding lesion on an ultrasonic tomographic image by displaying (or superimposing), on the ultrasonic tomographic image, information relating to the position of a lesion indicated on a three-dimensional image (for example, captured by the X-ray CT apparatus). More specifically, the processing discussed in Japanese Patent Application Laid-Open No. 2008-246264 includes obtaining the position of the ultrasonic tomographic image in the three-dimensional image space by performing positioning of the ultrasonic tomographic image relative to the three-dimensional image and drawing a boundary line, when the lesion of interest intersects with the ultrasonic cross section, on the ultrasonic tomographic image. In this case, a user can easily search for the corresponding lesion on the ultrasonic tomographic image that corresponds to the lesion of interest.
Further, as discussed in Japanese Patent Application Laid-Open No. 2008-212680, it is conventionally feasible to draw information representing the distance between a lesion of interest and an ultrasonic tomographic image, on the ultrasonic tomographic image, after completing the positioning of the ultrasonic tomographic image relative to a three-dimensional image.
However, in a case where an ultrasonic probe is used in the measurement of the position and orientation, a measurement value includes a significant error due to the accuracy of each probe. Further, the shape of a subject may vary due to the time difference between capturing of a reference image and capturing of an ultrasonic tomographic image. Therefore, a significant error is included in the estimated position of a corresponding lesion in a coordinate system that defines the ultrasonic tomographic image. In other words, the estimated position of the corresponding lesion tends to deviate from the actual position of the corresponding lesion. However, the above-described positional deviation is not taken into consideration in the conventional display discussed in Japanese Patent Application Laid-Open No. 2008-246264 or Japanese Patent Application Laid-Open No. 2008-212680. Accordingly, a user cannot identify (or cannot find) the corresponding lesion if the above-described positional deviation becomes larger. In this case, the user is forced to search the entire ultrasonic tomographic image to identify the corresponding lesion. As a result, the search efficiency decreases.
In a case where the conventional technique discussed in Japanese Patent Application Laid-Open No. 2008-246264 is employed, if the positioning of the ultrasonic tomographic image relative to the three-dimensional image has been performed without any error (i.e., in an ideal environment), the corresponding lesion exists in the drawn region. However, the actual positioning includes an error. Therefore, the corresponding lesion may exist in the vicinity of the drawn region. Hence, it is necessary for the operator to visually find the corresponding lesion in a relatively wide region including the drawn region and its vicinity. In this case, determining the search range appropriately considering the error is not so easy for the operator if the experience of the operator itself is insufficient.
Further, in a case where the conventional technique discussed in Japanese Patent Application Laid-Open No. 2008-212680 is employed, although it is possible for the operator to check the distance between the present cross section and the position of the corresponding lesion, determining the search range appropriately considering the error is not so easy for the operator if the experience of the operator itself is insufficient.